Hydropneumatic pumping unit



July 21, 1953 1 DWIGHT ALLER ETAL 2,645,899

HYDROPNEUMATIC PUMPING UNIT 6 Sheets-Sheet l Filed Deo. 6, 1950 Sd n ma Nu. E0 WN 1f. .w m ,n 1J l July 21, 1953 r DWIGHT ALLER ETAL 2,645,899

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HYDROPNEUMATIC PUMPING UNIT Filed Dec. 6, 1950 6 Sheets-Sheet 4 July 2l, 1953 T DWIGHT ALLER er1-AL 2,645,899

HYDROPNEUMATIC PUMPING UNIT Filed Dec. 6, 1950 6 Sheets-Sheet 5 T;f5r0..... ,37" IT n' FeoMPu/VP *t* Pam-(10550 9;! UMH/MP l l rlfI/w 97% di y! 96 Y f@ FIE- 4- 90'/ J T0 PUMP ,0,4m E /Vaa and By.- TZPW/G/f Huge,

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Patented July 2l, 1953 T Dwight Aller, san Gabriel, anaraui E. Non, Pasadena, Calif., assignors to United States Steel Corporation, a corporation of New Jersey Application December 6, 1950, Serial No. 199,504

7 Claims. 1

This invention Yrelates to improvements in hydro-pneumatic pumping units for oil wells.

Hydro-pneumatic pumping units commonly comprise a reciprocable duid operated rain, to which a sucker rod string is connected, la motivating pump for applying hydraulic pressure to the ram, an appropriate system of reversing valves, and a prime mover for driving the puinpl It is usual to counterbalance the ram with ya force equal approximately to the weight of the rod string plus half the weight of the column of oil pumped from the well and thus to equalize the load on the motivating pump and the' prime mover during the up and downstrokes of the ram. Such units have an advantage over themore common walking beam units that they 'furnish a longer stroke and thus necessitate fewer reversals and impose less severe stresses on the They also furnish a better control of A further object of the invention is to provide 4 improved pumping units which have the foregoing features and in which the reciprocations of the ram control the output of the 'reversible variable volume pump through a pilot valve, a pilot operated reversing valve and a 'servo motor, thereby positively interrelating pump output with the direction of movement and position of the ram.

Figures 4 and 5 are somewhat schematic views on a larger scale ofthe pilot valve and pilot oper ated reversing valve showing respectively their positions for an'upstroke and for -a downstroke of the ram; c c "1 Figure 6 is avertical sectional view on a larger scale of th'econnection between the counterl balance tank and the main cylinder;

A further object of the invention is to provide y improved pumping units in which the controls g of acceleration, speed and deceleration of the ram 1 on its upstroke and downstroke are independentl more siii-` invention, we have provided improved details of structure, a preferred form of which is shown` in the accompanying drawings in which:

Figure 1 is a side elevational view of an improved pumping unit which embodies features of the present invention; i

Figures 2a and 2b together are a schematic view of the hydraulic circuit for operating the pumping unit of Figure 1;

Figure 3 is a somewhat schematic view on a larger scale of a preferred construction or" motiu vating pump and manual reversing valve;

`Figures '7 and 8 are end elevational and vertical sectional views respectively on a larger scale of the servo control mechanism for the motivatingvk pump; and

Figure 10 is a vertical sectional view of ya detail of the control rod which operates the servo cam and the pilot valve;

The pumping unit of the present invention comprises a ram II) rand a counterbalance I2 which -preferably are substantially like those shown in our co-pending application Serial No. 58,714, iiled November 6, 1948 l(now Patent No. 2,572,748, issued October 23, 1951),` except that we have included refinements in the valve which closes off the counterbalance pressure in the event of rod lbreakage and in the means for lubricating the chain and sprockets.

Briefly, the ram includes a piston I3, which is reciprocable in a main cylinder I4, and a sprocket head I5 which carries sprockets I6 and I'I (Figures 1 and 217).. A chain I8 is dead-ended to a rod I9, passes over said sprockets, and is connected at `its other .end to the sucker rod string. This double reeving of the chain imparts to the rod string a stroke double the lengthv of the ram stroke. Piston I3 has a central bore through which extends an upstanding tube ZG. To produce an upstroke of the ram, a motivating pump, hereinafter described, delivers hydraulic uid into tube 2i) via a delivery pipe 2| and such uid acts on an efiectivefarea X o i the ram head. To produce a downstroke, the motivating pump delivers Afluid into cylinder, I4 via a delivery pipe yond the stroke limits of the piston to furnish adash-pot or cushioning eiect, as known in the art. vThe,hydraulic fluid isV an oil and is used alsoto,lubricate,variousk parts yof the unit, as hereinafter explained. c v

The counterbalancegi 2 includes a tank 23 and a l pipe 24 which connects the lower portion of said tank and the lower portion of cylinder I4 and normally furnishes free communication. Pipe 24, the lower portion of tank 23, and the portion of cylinder I4 below piston I3 contain hydraulic fluid. The upper portion of tank 23 contains air under pressure. The pressure of this air acts continuously on the bottom of piston I3 and thus tends to lift the ram and the rod string.

Pipe 24 contains a valve 25 for closing off counterbalance pressure from the ram cylinder in the event of a sudden release of theloadonY the ram, such as would occur if either the rod string or chain I8 breaks. ance pressure could drive the ram to the top of the cylinder with a destructivev force. Figurel 6 shows the details of this valve. Pipe 24. has avalve seat 26 at its juncture with tank 20 and an elbow bend 21 in line with said seat. A guide 28 is supported from the inside wall of the pipe and slidably supports a valve stem 29, which has a valve disk 30 atA its end cooperable with. seat 26. Stem 29 carries a collar 3| which engages guide 28 to limit the open position of thevalve. At its elbow 21 pipe 24 carries an outwardly extending tube 32, within which the back end of valve stem 29 nts closely. This end of stem 29 has a bore 33 which contains a. compression spring 34 that normally holds the valve disk unseated. The back end of tube 32 has a counterbore 35 and a closure plug. 36; A pipe 31, which has a fixed orifice 38 and a normally closed valve 39, connects tank 23 and counterbore 35. A pipe 40, which has a normally open valve 4I, connects pipes 24 and 31 and thus bal-- ances the static pressures on opposite ends of valve stem 29 and disk 3U.

If there is a sudden release of force on the ram, uid from tank 23 surges against valve disk 3U and pushes this disk against its seat 26, and thus closes off counterbalance pressure from the ram. Stem 29 forces uid from tube 32 via pipe 31, orifice 38, pipe 40 and valve 4I into pipe 24. The orifice cushions seating of the valve disk,

since it restricts ow of fluid from tube 32v behind the valve stem. Once the disk seats, the counterbalance pressure holds it seated, since the back of the disk and stem no longer are subjected to counterbalance pressure. The valve disk can be unseated for resumption of normal operation by opening valve 39 and thus again applying counterbalance pressure: to the back of the valve disk and stem.

In accordance with the present invention, tube 32 carries an electric switch 42 which has a spring pressed plunger 43 extending into the interior of the tube. When valve stem 29 moves into the tube as the valve disk seats, it depresses this plunger and operates the switch. The switch then stops the prime mover which drives the motivating pump, thus immediately halting delivery of hydraulic fluid from the motivating pump to the ram..

A pipe 44, which has a normally closed valve 45, connects cylinder I4 below piston I3 with the main fluid reservoir, hereinafter described. A pipe 46, which has a normally closed valve 41, connects counterbore 35 and pipe 44. Opening of valve 41, after closing valve 4I, relieves the static pressure behind valve stem 29 and thus furnishes a means for closing valve 25 manually. A pipe 48 connects pipes 24 and 44 and contains a check valve 49 which allows ow only from the former to the latter. This pipe furnishes an inlet for counterbalance` fluid t Otherwisel the counterbal.-

' the ends of: said` pipes.

cylinder I4 when the ram overtravels pipe 24.

Also in accordance with the present invention, the ram head I5 carries a lubricant tank 50 (Figure 2b). A pipe 5I, which contains a float valve 52, bleeds a small amount of hydraulic uid from the interior of the ram into said tank. The fluid level in said tank controls opening and closing of said iloat valve and thus controls the admission of more fluid. Lubricant flows gravitationally from said tank through pipes 53 to the bearings of sprockets I6 and I1. Lubricant Y also fiows-grav-itationally from said tank through pipes 54 and needle valves 55 to brushes 56 at These brushes contact chain I8 and thus lubricate it.

In accordance'with the present invention, the unithasa motivating pump 51 which is of the reversible variable volume type. Figure 2a illustrates this pump schematically and Figure 3 illustrates a preferred construction somewhat more in detail. The pump illustrated has a casing 58, a pintle 59 xed in said casing, a cylinder block 60 rotatable around said pintle, a slide block 6I slidable across said casing, and a thrust ringr 62 within said slide block and surrounding said cylinder block. The cylinder block contains a plurality' of radial cylinders 63 which have pistons 64. The pintle has two delivery ports A and B connected respectively to delivery pipes 2I and 22. The pump has a mainreservoir 65. A prime mover P (Figure l) rotates the cylinder block clockwise as viewed in Figure 3. When the slide block is to the right of center, the pump delivers fluid through port A, delivery pipe 2| and tube 20 to the inside of ram I0 and the ram makes an upstroke. When the slide block is centered, there is no delivery. When the slide block is to the left of center, the pump delivers fluid through port B and delivery pipe 22 into cylinder I4 and the ram makes a downstroke. The farther the slide block is off center in either direction, the greater the delivery and the greater the speed with which the pump propels the ram. Inasmuch as pumps of this construction per se are well known, no more detailed description is deemed necessary.

For positioning the slide block 6I in the pump casing 58, the casing has a cylinder 66 at the left and a cylinder 61 at the right (Figure 3). The slide block has positioning pistons 68 and 69 at opposite ends slidably received in said cylinders. Piston 69 at the right has a greater facial area than piston 68 at the left. Beyond cylinder 66 at the left the casing has a bore 10 which contains a slidable stem 1I coupled with piston 68. A cap 12 closes the end of bore 10 and carries an inwardly projecting headed spindle 13. 'I'he outer end of stem 1I carries a hook device 14 which engages over the head of said spindle. This engagement limits the extreme position to which the slide block can move to the right, and this position can be adjusted by moving cap 12, Beyond cylinder `61 at the right the casing has a bore 15 which contains a rotatable servo shaft 16 which limits the extreme position to which the slide block can move to the left in a manner hereinafter explained.

The pump casing 58 contains an auxiliary gear pump 11 driven by the prime mover for supplying pilot pressure to the various pilot operated parts, including cylinders 66 and 61. The pump casing has a suction duct 18 from reservoir 65 to auxiliary pump 11, and an outlet duct 19 from the auxiliary pump. Duct 19 has a connection to a relief valve which holds the pressure in this duct to a predetermined'value (e. g. 130 p, s.' 1.),

designated high pilot pressure. which contains a check valve 82, connects duct 19 and cylinder 66 so that piston 68 on the left is always subject to high pilot pressure.

The unit comprises a pilot operated reversing valve 83 (Figures 2a, 4 and 5), a manual reversing valve S4 (Figures 2a and 3), and a pilot valve 85 (Figures 2b, 4 and 5), A pipe 86 connects pipe 8| and pilot valve 85. Figure 4 illustrates the position of valves 83 and 85 when the motivating pump is delivering fluid through pipe 2| andthe ram is making an upstroke.k In this position pilot valvel 85 connects pipe 86 which comes from the auxiliary pump with a pipe 81 which extends to the right end of the pilot voperated reversing valve 83. At the same time the pilot valve connects a pipe 88, which extends from the left end of said reversing valve, with a pipe 89 which connects with pipe 44 and thence to reservoir 65. The pilot operated reversing valve 83 contains a reciprocable valve spool 90, and it has four ports 9|, 92, 93 and 94. A pipe 95 connects pipe 86 from the auxiliary pump with port 9 I. A pipe 96 connects port 93 with the manual reversing valve "84 hereinafter described. A pipe 91 connects port 92 with said manual reversing valve. A pipe 98 connects port 94 with pipe 44 and thence with reservoir 65.

In the position of the parts just described, pilot valve 85 directs fluid at high pilot pressure from auxiliary pump 11 to the right end of valve spool and relieves the left end sorthat this spool is all the way to the left. The pilot operated revel-sing valve connects pipe 95 with pipe 96. Normally the manual reversing valve blocks oif pipe 96 so there is no flow through this part of the circuit. A pipe 99, which contains a check valve |90 and an adjustable throttling valve |0|, connects cylinder 61 and the manual reversing valve, which normally connects this pipe with pipe 91. The pilot operated reversing valve also connects pipe 91 with pipe 98 and thus relieves cylinder 61. Therefore the pressure in cylinder 66 keeps slide block 6| of the motivating pump to the right to the limit which engagement of hook device 14 with spindle 13 permits, which as already explained is the position in which the pump delivers iiuid through pipe 2| and the ram makes an upstroke.

Sprocket head carries a depending control rod |02 to which are adjustably affixed an upper pilot valve trip |03, a lower pilot valve trip |04, and a servo linkage cam |95 (Figures l and 2b). Adjustment of the position of these parts on the rod determines the reversal points. Since the ram moves relatively slowly it is possible to adjust these parts while the lram is in motion, and thus to obtain a very precise control of the bottom reversal point. When the ram completes its upstroke, the lower trip |04 trips pilot valve 85 'to a position in which it connects pipe 86 with pipe 88 and also connects pipe 81 with pipe 89. Figure 5 shows the position the pilot valve and pilot y operated reversing valve now assume. The left end of spool 90 of the pilot operated reversing valve is subjected to hydraulic fluid under high pilot pressure and the right end is relieved,

charges through port 92, passes through manual v reversing valve 84, pipe 99, a check valve |06, which shunts throttling valve |0I, and through a pipe |01, which connects pipe 99 and cylinder 61, shunting check valve |00 (Figure 3).` Ports 93 and 94 of thepilot OperatedreVerSing' valve also are connected, but normally there is no fluid circulation through these ports.

Pump casing 58 has a duct |08 to which pipe |01 is connected and which extends to an annular l groove |09 in the wall of bore 15. This groove surrounds servo shaft 16,`hereinbefore referred to. The servo shaft has a radial duct H0, which communicatesr with groove |09, a longitudinal duct which communicates with said radial duct, and a second radial duct ||2, which communicates with said longitudinal duct (Figure 8).

The servo shaft has two spiral grooves ||3 land ||4 and a spiral land ||5 betwen them. Groove lic fluid under high pilot pressure to pipe |01,Y

such fluid enters cylinder 61 via duct |08, annular groove |09, ducts ||0, and ||2, "spiral groove ||3 and duct ||6. Since piston 69 has a greater facial area than piston 68, the slide block moves to the left'. During such movement fluid escapes from cylinder 66 via means hereinafter described. The movement continues until ductA IIB has moved to closes it off.

It is kseen that rotation of servo shaft 16 clocka position in which land ||5 A wise, as viewed vin Figure 7, in effect shifts grooves |53 and ||4 and land ||5 tothe right, and rota tion counterclockwise in effect shifts them to the left. If the servo shaft is rotated clockwise, thun moving groove ||4 to the right into communication with duct IIS, cylinder 61 is relieved to the interior of the pump casing and high pilot pressure on piston 618 forces the slide block to the right. If the servo shaft is rotated counterclockwise, thus moving groove 3 tothe left into communication with the duct H6, more fluid is admitted to cylinder 61 and forces the slide block to theleft. The net effect is that as long as this cylinder is subjected to pressure, duct ||6 in piston 69. follows land l5. The position of rotation of the servo shaft thus determinesthe positionwhich the slide block occupies and, whenever the servo shaft rotates clockwise or counterclockwise,

the slide block moves ,correspondingly to the right or left. v

The means through which uid escapes from cylinder 66 as the slide block 6| moves to the left include longitudinal and radial ducts |1 and |.8-

and an annular groove ||9 in spindle 1|, a pair of annular grooves |20 and |2| in the wall of bore 10 in the pump casing, a pair of ducts |22 and |23 communicating with the latter annular grooves, and pipes |24 and |25 communicating with the Ilatter ducts .and extending to pipe 95.

Pipe |24 has Ian adjustable throttling valve |26 and pipe |25 an adjustable throttling valve |21. When the slide block is in its extreme position to the right, annular groove |9 in stem 1| com.- municates with annular groove 20, `duct |22 and pipe |24.` The throttling valve |26 thus controls the rateof escape of iiuid from cylinder 66 as the slide block moves from this position to its centered position and thereby controls the rate of deceleration of ther ram as it approaches thetop of its upstroke. As the slide block passes its `centered position; annular groove ||9 in stem 1| 7.. passesfrom communication with annular groove |20 into communication with annular groove |2| and with duct |23 and pipe |25. Ihethrottling valve |21 thus controls the rate of escape of fluid from cylinder 66V as the slide block moves from its centered positionr to its position at the extreme left and thereby controls the rate of acceleration of the ram as it starts its downstroke.

The outer end of servo shaft 16 carries a lever |28 (Figure 7). Pump-casing 58 has an adjustable stop |29 with which lever |28 is engageable, and a spring |30'urges the lever into engagement with this stop. Thisstop thus limitsthe counterolockwise rotation of the servo shaft, and therefore limits the extreme position to which the slide block can move to the left. A linkage |3| is connected to lever |28 and extends to another lever |32 which is positioned to cooperate with cam on control rod |02 (Figures 1 and 2b). As the ram approaches the end of its downstroke, cam |05 engages lever |32 and thus turns this lever counterclockwise, 'as viewed in Figure 1, and lever |28 clockwise, as viewed in Figure 7. Clockwise rotation of the latter lever turns. servo shaft 16 clockwise and, as already explained, in effectshifts its land ||5 to the right. Thereupon slide block 6| moves to the right, the pump output diminishes, and the ram decelerates. The position and shape of cam |05 control the rate of deceleration.

Shortly the upper pilot valve trip |03 on control rod |02 trips pilot valve 05 and the parts return to the position first described and another upstroke begins. Throttling valve |0| controls the rate of escape of fluid from cylinder 61 and thus. controls the rate of acceleration of the ram at the start of its upstroke.

As already described, the output from gear pump 11 passes into a duct 19 which communicates with a relief valve 80. The excess fluid which discharges through this relief valve flows into a duct |33 which has a second relief -valve |34 (Figure 3). This latter relief valve regulates the pressure in duct |33 to a predetermined value (e. g. 100 p. s. i.) designated"medium pilot pressure." Fluid under medium pilot pressure flows from duct |33 through a pipe |35 to an oil cooler |36 and an oil filter |31 connected in parallel (Figure 2a). Fluid discharges from the filter into pipe 44 which returns it to the main reservoir 65.

Fluid discharges from the cooler through a pipe |38 which extends to two check valves |39 and |40 (Figures 2a and 3). Check valve |39 connects pipe |38 and the pump delivery pipe 2|, while check valve |40 connects pipe |38 and the other pump delivery pipe 22. These check valves introduce fluid to whichever of the delivery pipes is lacting as a return from the ram to the motivating pump and thus supercharge the pump. A back pressure relief valve |4|, hereinafter described, maintains the fluid in the low pressure side of the pump and in pipe |38 at a predetermined pressure (e. g. 60 p. s. i.) designated low pilot pressure.

The motivating pump is equipped also with a suction valve which has a spring centered spool |42, a passage |43 extending into the main reservoir 65, and a check valve |44 closing said passage against return of fluid to the reservoir (Figure 3). The pump casing has a duct |45, which extends from its delivery port A to the right end of valve spool |42, and a duct |46, which extends from its delivery port B to the left end of this valve. spool. Whenl the pump delivers fluid from port'A; fluidpressure in ductA |45-forces the valve spool to the left and opens duct |46 so that fluid can be supplied to port B, which is now the low pressure or suction side of the pump, from the reservoir via check valve |44, passage |43 and duct |46'. The reverse takes place when the pump delivers fluidr from port B. The back pressure relief valve |4|, hereinbefore referred to, communicates with passage |43 and with whichever of ducts |45 or |46 is open thereto.

'I'he pump casing also contains relief valves |41 andV |48A in ducts |45 and |46 respectively. Ducts |49 and |50 extend from said relief valves to a common duct |5|, and thence to the main re'servoir 65. If the pressure in the high pressure or delivery side of the pump is excessive, fluid escapes via. the relief valve on this side and its associated ducts.

A start-stop valve |52 is connected across delivery pipes 2| and 22 (Figure 2a). During normal operation of the unit this valve is closed. When it is open, it short circuits the delivery pipes and thus stops delivery of fluid to the ram.

The unit has an air make-up pump |53, the details of which are shown in Figure 9. Pump |53 includes a cylinder |54 which contains a recipro- -cable piston |55. Cylinder |54 has an air intake 4port |56, an air discharge port |51, and power fluid ports '|58 and |59. A pipe |60, which contains a check valve 6| (Figure 2a), a normally open valve |62 (Figure 2b) and a pressure gauge |03 (Figure 2b), connects port |51 and counterbalance tank 23. A `pipe |64 connects the power fluid port |58 with delivery pipe 2| and a pipe |65 connects the power fluid port |59 with delivery pipe 22. The air intake port |56 is equipped with a check valve |66. When the motivating pump 51 delivers fluid through pipe 2|, some fluid enters cylinder |54 of pump |53 via pipe |64 and forces piston |55 upwardly and discharges the air in the cylinder through pipe |60 into the counterbalance tank. When the motivating pump delivers fluid through pipe 22, some fluid enters cylinder |54 via pipe |65 and forces the piston back and allows air to flow into the cylinder via air intake |56. The counterbalance tank has a relief valve |61 to protect it against excessive pressures (Figure 2b). Preferably a nitrogen or compressed air bottle |68 is connected to pipe |60 to furnish a pressure source for initially charging the counterbalance tank (Figure 2a).

For introducing hydraulic fluid to the counterbalance tank, the unit has a pipe |69 which is connected to delivery pipe 22 and contains a normally closed valve |10 (Figure 2b) When valve |10 is open, the motivating pump delivers hydraulic fluid to the counterbalance tank via pipes 22 and |69.

A pipe |1I is connected to the counterbalance tank to prevent the accumulation of excessive fluid in this tank and thus depriving the main reservoir. The tendency is for fluid to build up in the tank because of leakage past piston I3. Pipe |1| extends to a float operated control valve |12 in a fluid level tank |13. A return pipe |14 returns fluid from said tank to the main reservoir 65. As the fluid level in reservoir 65 drops, there is a corresponding drop in the fluid level in tank |13. Such a drop opens valve |12, whereupon air pressure in the counterbalance tank forces fluid through pipe |1| into tank |13.

Figure 3 shows the manual reversing valve 94 in the position it occupies during normal operationV of the unit. In this position the valve serves merelyy as a conduit connecting pipes 91 and 99.

f 9 This Valve has a spool and ports |16, |11, |18 and |19. A pipe |80 connects port |16, and rpipe 44 which extends to the main reservoir 65. This connection serves to` return fluid which leaks around spool |15 to the reservoir. nected tov port I 11, pipe 99 to port |18, and pipe 91 to port |19. The normal position of spool |15 is tothe right in the valve housing.

If the operator desires to reverse the direction of movement of the ram during either stroke, he simply moves spool |15 of the manual reversing valve to the left. The valve then connects pipes 96 and 99 and blocks oii pipe 91. If the ram is making an upstroke :atthe moment, the gear pump 11 commences delivering fluid under high pilot pressure through pipe 96, ports |11 andi 18, pipe 99 and thence to cylinderv 61. f Thereupon the slide block 6| of the motivating pump moves to the left, the pump reverses Vits delivery and the ram starts moving downwardly. If the ram is making a downstroke at the moment, cylinder 61 is relieved via pipe 99, ports |18 and |11, pipe 96, ports 93 and 94 of the pilot operated reversing valve 83, and pipes 98 and 44 tothe main reservoir 85. Thereupon slide block 6| moves to the right, the pump reverses its delivery, and thev ram starts moving upwardly. t

'Figure 10 shows in detail a preferred construction of-control rod l2forenabling the servo cam |95 and upper trip=|93rto be adjusted vertically' rPipe 96 is con- 1V Whenthe ram nears completion of its down- Such rotation moves the from the motivating pumpy diminishesmthus decelerating the ram.v Then the upper pilotvalve trip |93 trips pilot valve 85, which again changes -the direction of applicationof pilot pressure to the pilot operated reversingvalve 83;` Thereupon the right side of the slide block is relieved and the slide block moves allthe Way tothe right and the ram starts another upstroke.

It is seen that positonof hook device 14 con .trols vthe speedof the ram during its upstroke, since engagement of stem 1| with said hook device limitsthe 'extreme position to which slide block 6| can move to the right.. The position of the stop |29 for lever |28 controls the speed of the ram during its downstroke, since this stop while the unit is'operating. Said control rod inflange |84 at its lower end. i Spindle |82 has'a series of tapped openings |85 adjacent its upper end. The upper trip finger |93 can be fixed in any of said taps and extendsthrough slot |83. n

The spindle has a screw-threaded section |86 which carries a nut |81.

|88 normally hold nut |81 against flange |84..v A set screw |89 in tubular element |8| also assists in holding the spindle in position. t The lower end of the spindle carries theservo cam |05 and also a guide|99which .slides up and down on the dead end rod I9.

It is highly desirable that the clearance in the subsurface pump be as smallas practicable. The position of cam |85 and trip |83 determines the bottom reversalpoint and therefore determines this clearance.Y Their position can be adjusted by loosening screws |88 and set screw |89 and then rotating nut |81 with respect to spindle |82. Since the control rod moves slowly at only about half the speed of the polished rod, r'this adjustment can be made while the unit is in operation.

Operation The .operation of a hydro-pneumatic pumping unit constructed as just described can be summari'zed as follows:

j When the ram |8 is making an upstroke, the reversible yvariable volumemotivating pump is delivering hydraulic fluid through deliveryvpipev A plurality of screws.v

motivating pump starts delivering iiuid through celeration of the ram at the bottom of its downj l stroke. The'opening of throttling valve |0| controls acceleration of the ram atthe start of its upstroke. The position of thetrips on the con- 'trol rod controls the reversal points. Therefore all these controls are entirely 4independent of each other and any can be adjusted without affecting the others. f f

The control rod |.02which operates` the pilot `valve and the servomotor is 'carried bythe ram 'and always moves therewith. This arrangement positively interrelates operation of the motivating pump with the position and direction of movement of the ram', as distinguished from anl movement in said cylinder, means `for connecting a string of sucker rods to said ram, pneumatic means for applying a counterbalancing force rto :said ram, a reversible variable volume motivating pump having delivery pipes connected to said cylinder for supplying hydraulic fluid to reciprocate said ram and including a slide block having an off-center position in which said motivating ypump delivers fluid to said cylinder to produce an l.upstroke of the ram, a centered position in .which said motivating pump delivers no fluid, and .a second off-'center position 'in which said kmotivating pumpfd'elivers fluid to said cylinder to produce a downstroke of the ram, the distance olf-center of said slide block in eitherdirection determining the volume of fluid which said motivating pump delivers, positioning pistons and cylinders at opposite ends of said slide block, a pilot circuit connected to said positioning cylinders and including an auxiliary pump for supplying hydraulic fluid thereto under pilot pressure, one of said positioning cylinders kbeing of smaller cross-sectional area than the other and n vemigrato V1 l being subjected constantly to iluid under pilot pressure, a pilot operated reversing valve in said pilot circuit for controlling the application of iluid under pilot pressure to the other positioning cylinder, a, servo motor for positioning the piston in this other positioning cylinder when the cylinder is subjected to pilot pressure, escape pipes from both said positioning cylinders, a pilot valve in said pilot circuit for controlling said reversing valve, a linkage for controlling said servo motor, means on said ram for shifting said pilot valve at the ends of the ram strokes and thereby moving said reversing valve to its other off-center position, means on said ram for operating the linkage of said servo motor on the ram downstroke in advance of said pilot valve and thereby decelerating the ram, and means in said escape pipes controlling escape of fluid therethrough and thereby controlling deceleration of the ram at the end of its upstroke andacceleracenter position, thereby furnishing independent controls for deceleration of the ram at the end of its upstroke and for acceleration of the ram at the beginning of its downstroke.

3. A hydro-pneumatic pumping unit as deilned in claim 1 in which there is a manual reversing valve between said pilot operated reversing valve and said motivating pump, actuation of said manual reversing valve reversing said motivating pump before the ram reaches the end of its stroke.

4. A hydro-pneumatic pumping unit comprising a cylinder, a ram carried for reciprocable movement in said cylinder and havinga sprocket head at its upper end and a pair of sprockets rotatably mountedin said sprocket head. a chain having one of its ends dead-ended, passing over said sprockets and adapted to be connected` at its other end to a sucker rod string, means for applying a counterbalancing force to said ram, a

motivating pump having delivery pipes connected to said cylinder for supplying hydraulic uid to reciprocate said ram, a lubricant tank in said sprocket head, a conduit to deliver hydraulic fluid from said ram to said lubricant tank, a float valve regulating the level of fluid in said tank, and conduits to lubricate said chain and said sprockets gravitationally from said lubricant tank.

5. A hydro-pneumatic pumping unit comprising a cylinder, a Vram carried for reciprocable movement in said cylinder, means for connecting a string of sucker rods to said ram, pneumatic means for applying acounterbalancing force to said ram, a valve for automatically shutting off this counterbalancing force in the event of a sudden release of the load on the ram, a motivating pump having delivery pipes connected to .said cylinder for supplying hydraulic fluid to reciprocate said ram, and electric switch means operated :by said valve for :automatically stopping said motivating pump when said valve shuts off the counterbalancing force 'from said ram.

6. In a hydro-pneumatic pumping unit which includes a cylinder, a ram carried for reciprocable movement in said cy1inder,.means for connecting a string of sucker `rods to said ram, means for counterbalancing said ram, a Vmotivating pump for delivering vhydraulic fluidto said cylinder, and valves and a cam operated linkage for controlling the output of said motivating pump, the combination with saidram oi a control rod which depends therefrom and comprises a tubular element `having a slot, a spindle telescoping into said tubular element and carrying a trip finger which extends through said slot for operating one of said valves and a cam adjacent its lower end for operating said linkage, and means adjustably vxing said spindle to said tubular element to vpermit relative adjustment while the unit is in operation'to vary the bottom reversal point of said ram.

,7. In a hydro-pneumatic pumping unit which includes a cylindena ram carried for reciprocable movement in said cylinder, means forconnecting a string of sucker rods to said ram,means for counterbalancingsaid ram, a motivating pump for delivering hydraulic iluid to said cylinder, and valves anda cam operated linkage for controllingzthe output of said motivating pump, the combination with said ram of a controlrod which dependstherefrom and Ycomprises a ltubular element having a `slot `in its upper portion'and-a flange onits lower end, a'spindle ,telescoping into said tubular 'element and carrying a trip finger which extendsthrongh said slot for operating one of said valves and a cam adjacent its lower end for operating .said linkage, said spindle having a screw-threaded section. a nut movably carried on said screw-threaded section and abutting said iiange, and screw means releasably ilxing said spindle in adjustedposition-with respect to said tubular element, said spindle being adjustable on release of said screw means and movement of said nutvwhile the unit is'in operation to vary the bottom;reversal .point o! said ram.

T DWIGHT ALLER.

PAUL E. NOLL.

References Cited in the le `of this patent UNITED lSTATES yPATENTS Number Name Date 1,619,474 Hubbard Mar. 1, 1927 2,027,104 Kahr .et a1 Jan. 7, 1936 2,093,690 Wiedmann Sept. 21, 1937 2,114,005 Tyler Apr. 12, 1938 2,227,814 Tyler Jan. 7, 1941 2,273,721 Muller Feb. 17, 1942 `2,331,046 Robinson Oct. 5, 1943 2,367,248 Vickers Jan. 16, 1945 2,432,305 Geiger Dec. 9, 1947 2,443,301 Conabee June l5, 1948 2,564,285 Smith Aug. 14, 1951 

